Combined isomerization process



May 31, 1960 R. A. FINDLAY COMBINED IsoMERIzAu-ION PRocEss Filed June 9, 1958 A 7` TORNEKS mmSr .w mm2/zml om mzbm .m A mw wv) 5.5.63 Tm mm2/Fam m A. f y ma. ,f mzrm/ lzmoz f\ m m myV/Imm @m @n M G m mm 3 W moom .GIE E wznmm. \1 mm mm f x J m m j d: :mman mm Nm o.) Juv mm mm m /5 u l f n. A wm) vm mm vm) u wv mznm om S vv t? m. mv

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with the heavier normal paraflins 2,938,935 COMBINED ISOMERIZATION PROCESS Robert A. Findlay, Bartlesville, Okla., assigner to Phillips Petroleum Company,*a corporation of Delaware Filed June 9, 1958, Ser. No. 740,729 9 Claims. (Cl. 260683.67)

This invention relates to a combination process for isomerizing normal butane and normally liquid parallinic hydrocarbons. in another aspect, it relates to an irnproved method for maintaining a low temperature in the isomerization of parains` having from to 12 carbon atoms per molecule in the presence of isobutane. In one of its more specic aspects, this invention relates to an improved combination process for isomerizng normal butane and using the isobutane product in the isomerization of normal hexane or heptane at a relatively low temperature.

The upgrading of hydrocarbons in the gasoline boiling range to high octane components by isomerizationy of normal paratlins with aluminum halide-hydrocarbon complex catalyst is well known. From an economic standpoint one of the chief difliculties in such processes is the conservation of catalyst which tends to degrade or lose its activity by complexing with hydrocarbons present in the reaction. One method of reducing catalyst consumption in such reactions involves the use of isobutane in mixture undergoing isomerization. Such a process and its advantages are described in a copending application of H. J. Hepp and L. E. Drehman, Serial No. 742,257, filed June 16, 1958. It is further advantageous to conduct such isomerizations in the presence of .isobutane at relatively low temperatures and thereby reduce catalyst consumption and decrease the alkylation of isobutane with the heavier paratlns. Since these isomerization reactions are exothermic, the use ofI refrigerants has beenrequired to cool recycle streams of the reaction mixture.

According to my invention a combination isomerization of normal butano and of heavier paratlinic hydrocarbons in the presence of isobutane is provided in which relatively low temperatures, as will subsequently be explained, can be maintained without the necessity of employing refrigerants. Broadly, my invention is the uniqueY combination of two isomerization processes in which butane is isomerized to isobutane by contact with an aluminum halide catalyst in the presence of hydrogen chloride, the isobutane product is cooled by autorefrigeration and introduced into a second isomerization zone wherein heavier parainic hydrocarbons are isomerized in the presence of an aluminum halide-hydrocarbon complex and hydrogen chloride, and theeluent of the second isomerization zone is autorefrigerated and' employed to precool the parainic feed. By condensing the vapors formed in the second autorefrigeration step and recycling the condensate to the second isomerization zone, the necessity of refrigerant is eliminated.

y It is an object of this invention to provide an improved combination isomerization process for the production of high octane gasoline. Itis another object ofl my invention to provide a method for maintaining a relatively low' temperature in a liquid phase isomerization process with-- out the necessity of using a refrigerant. Still another lobject is to provide an improved hydrocarbon isomerization; process inwhich consumption of the 'aluminum halide 2,938,935 Patented May 31, 1960l catalyst is held to a minimum. Other and further objects of my invention will be apparent to those skilled in the' art from the `following description and drawing which is a schematic ow diagram of the preferred manner in which the above mentioned isomerization process are combined in my invention.

The process of my invention presents a method for upgrading normally liquid straight chain or slightly branched paraiiinic hydrocarbons to more highly. branched hydrocarbons by contacting these paraflins with an aluminum halide hydrocarbon complex catalyst in the presence of isobutane. The isobutane is formed in a vapor phase process, preferably using a fixed catalyst bed. Although not preferred, a liquid phase butane isomerization can be used with high pressures and the eluent cooled by flashing. TheV heavier paraflinc hydrocarbons are iso- `merized Vin the liquid phase at relatively low temperatures.

The isomerization catalyst used for these isomerization reactions is preferably aluminum chloride although aluminum bromidecan be used.

To describe my invention reference is made to the drawing which sets forth a preferred embodiment with operating variables which are meant to be exemplary and not limiting. Isobutane is formed in isomerization zone 10 to which normal butane is fed through line 11. This isomerization zone employs a fixed bed aluminum chloride catalyst supported on bauxite. Catalyst of this type generally contains about 5 weight percent aluminum chloride which is added by sublimation onto a fixed bauxite bed. .Aluminum chloride is added by sublimation as needed to restore the activity of the catalyst. Hydrogen chloride isalso employed as an activator in this reaction and is introduced to zone 10 through line 12. The temperatures of such isomerization processes range generally from about 225 F. when the catalyst is fresh to about 310 F. as the catalyst ages. 'Ihe pressure can vary broadly from 150 to 400 p.s.i.g. and the HC1 concentration, based upon feed, is in the range of 0.5 to 5 weight percent, generally about 2 to 3 weight percent. Residence timeof butane in the reaction zone varies from about 20. to 200 seconds With a feed space velocity of about 0.2 to 10 and preferably 0.3 to 1.0 volumes per volume of catalyst.

i The isomerization eluent containing isobutane, butane and hydrogen chloride passes from zone 10 lthrough line 13 and is condensed in condenser 14. The liquid condensate passes through valve 16 into flash -chamber 17l which is operated at a pressure of about 25 to 40 p.s.i.a. Hydrogen chloride is thus flashed from the etluent, passthrough line 18 overhead to compressor 19, which returns hydrogen chloride to 20 and lines 11 or' 12. The temperature of this hydrogen chloride stream will generally be in the range of about to 150 F.

In the condensation and flashing steps the isobutane product is reduced to about 50 to 75 F. and passes through line 21 to pump 22 and thence through line 23 to isomerization reactor 24. By employing the condenser on the vapor stream and the Hash step as above described, fractionation of the isomerization eluent is obviated. Furthermore, the necessity of guard chambers on the eluent stream is removed. Guard chambers of bauxite are generally necessary to remove aluminum chloride' carried over with the isomerization'efliuent in order to prevent fouling of the bubble plates in fractionation columns employed in conventional prior art systems.`Thus the use of the condenser and ash zone eliminates both the guard chambers and the fractionation column. AccumulationY of aluminum chloride in condenser 14 canfbe'- isomerization zone 10 through linetion. At the temperatures employed, condenser 14 can be cooled with water and refrigerant is not required.

Normal parans which contain from to 12 carbon atoms per molecule, preferably hexane or heptane, are introduced to theprocess through line 26 and pass through heat exchanger 27 where the 'temperature' of the feed is reduced to not over about 100 F. Such a cooling step is desirable, especially when the feed is provided directly from previous fractionation. This cooling can be readily effected according to my invention by heat transfer within the system as subsequently described. The cooled parafinic feed passes through line 28 and enters recycle loop 29 carrying aluminum chloride-hydrocarbon complex, sometimes called catalyst sludge in these processes. The reactants are thus introduced intoliquid phase isomerization zone 24 with the catalyst, the reaction vessel being equipped with mechanical stirring means 30.

This second stage isomerization can be carried out at a temperature in the range of about 30 to 150 F. and preferably, for maximum advantage of the combined process of my invention, the temperature is in the range of about 60 to 130 F. vwith the pressure sufficient to maintain the reactants in the liquid phase. The Visobutane stream in line 23 also contains a small amount of normal butane and hydrogen chloride. This is a further advantage since hydrogen chloride is desired in the second isomerization step, generally in a concentration of about 4 weight percent based on feed. The residence time in the reactor is broadly from about minutes to 2 hours and generally aboutV 30 minutes is suicient. When isomerizing heptane I prefer to employ an isobutane' to heptane ratio between 0.5 and 5 to l on a mol basis and preferably at least 1.1 mols of isobutane per mol of heptane. The hydrocarbon/ catalyst ratio is about 0.821 to about 5:1 with the preferred ratio being in the range of 1.5:1 to 3:1. The amount of aluminum halide in the complex can vary broadly but about 60 to 70 weight percent is preferred.

The reactant efuent is withdrawn from reactor 24 through line 31 and passed into settling tank 32 where the catalyst is permitted to settle and separate from the reaction mixture. The aluminum chloride catalyst is withdrawn from settling tank 32 and recycled to reactor 24 through loop 29 while the hydrocarbon product is passed through line 33 and valve 34 into flash vessel 36 operating at a pressure of about V18 to 20 p.s.i.a. By flashing the effluent stream in line 33 in this manner the product can be cooled by about 20 to 50 F. and withdrawn as liquid through line 37. This cooled product is passed by pump 38 through line 39 and heat exchanger 27 where the product serves to cool the paraffin feed as previously described.

The overhead vapors from flash vessel 36 pass byline 40 to compressor 41. These overhead vapors contain hydrogen chloride and isobutane and are compressed to a pressure slightly above that of isomerization zone 24. Fresh hydrogen chloride can be introduced into line 40 as desired through line 42. The compressed recycle vaporspass through line 43 and condenser 44 where they are condensed before being returned to vessel 24 by lines 46 and 23. Since a relatively hot vapor stream is being condensed in condenser 44, water can be used as coolant. The condensate will have a temperature of about 100 to about 110 F. at a pressure generally about 125 to 150 p.s.i.a. n

Y. Isomerized product leaves condenser 27 through line 47 and passes to fractionator 48 where a separation is made between the butanes and lighter materials `which pass yoverhead through line 49 and the pentanes and heavier materials which are taken off the bottom as product through line 50. The overhead vapors are again fractionated in fractionator 51 separating the normal butane vfrom isobutane and remaining hydrogen chloride which passes to fractionator 52 through line 53. The normal butane vis recycled to isomer-ization zone 10 4 through lines 54 and 11. The hydrogen chloride and isobutane in line 53 is again separated in fractionator 52, recovering isobutane substantially free of hydrogen chloride from the bottom of fractionator through line 56.

Hydrogen chloride and isobutane taken overhead through line 57 is compressed in compressor 5S and passes through line 59 to join the recycle stream in line 43, returning to reactor 24. It will be evident that fractionation zones 48, 51 and 52 can be combined into one or two fractionation columns using side draws for the yintermediate boiling range products. Separate zones are shown in `this drawing for simplicity.

The reactions taking place in reactor 24 can be referred i to as isoalkylation, as they include a considerable amount of disproportionation in addition to isomerization. In the presence of the high amount of isobutane described in the present invention, at least a part of the reaction is directed to the inter-action of isobutane and the higher paraffin to produce intermediate molecular weight hydrocarbons with a branched chain structure. As examples, isobutane and normal heptane will react to produce isopentane and isohexanes, and isobutane and normal hexane will react to produce isopentane. In the absence of isobutane, the process would produce a considerable amount of isobutane by disproportionation, but by the inclusion of isobutane in the feed, the production of isobutane can be controlled to the desired amount or stopped entirely. By the inclusion of enough isobutane in the feed, isobutaneV can actually be caused to be consumed with the formation of higher boiling parains. t

In the operation of the present process, the reaction vessel is ordinarily a mechanically stirred vessel operated under suicient pressure to maintain liquid phase. VStirring is effected to cause intimate contact of the catalyst phase and hydrocarbon phase and cause the reaction to proceed. Other reactors, such as jet agitated reactors,

can also be used.`

The normally liquid hydrocarbons used in the present process are the normal and/ or slightly branched paraiins, preferably having from 5 to l2 carbon atoms per molecule. Higher molecular weight materials can be used, however. The feed should be substantially free of Varomatics. Generally the aromaties should not exceed-about 0.3 volume percent ofthe hydrocarbon feed to the reaction. It is preferred that the hydrocarbon feed contain no more than 0.2 volume percent aromatics. These limits include both the isobutane and normally liquid hydrocarbon volumes. In reactions -where the catalyst employed in the'second isomerization nzone is to be used in an alkylation operation involving isobutane and ethyl* ene as described in the above mentioned copending application of H. J. Hepp and L. E. Drehman, it is preferred that the parafns employed in the feed stream to the isomerization zone have from 5 to 7 -carbon atoms per molecule and that the quantity of aromatics in the feed not exceed 0.2 volume percent and the naphthenes not exceed 5 to 10 volume percent. Complete removal of aromatics from the hydrocarbon feed is diicult from a processing standpoint, but it is desirable to maintain the aromatic concentration as low as practical operation permits. The effect of the aromatics on the reaction in the liquid phase isomerization zone is to inhibit the disproportionation reaction quite strongly and to slow down the isomerization reaction.

By observing the limit on aromatics in the feed, as above described, it is possible to obtain the desired reactions at temperatures in the range of 30 F. to 150 F., preferably 60 F. to 130 F., in reaction time-s asl low as 5 minutes. The reaction can be extended for several hours, although as stated above, the reaction time generally is about 10 minutes to 2 hours. The naphthenic hydrocarbon content of the hydrocarbon feed to the process is not as critical as the aromatic content, but it is preferably kept to a practical minimum. 1n most cases.

creases in aluminum chloride content, and at greater the naphthenes will be in a range of not more than about to l0 volume percent of the hydrocarbon feed. Increasing the severity of the reaction conditions by increasing temperature or reaction time enables a higher amount of aromatics to be tolerated. Also, increasing the amount of isobutane reduces the percentage of aromatics in-the total feed and thus increases the amount of aromatics that can be tolerated in the normal paraflin feed. Commercially available feedstocks should contain no more than about 1 percent of aromatics and 20 percent of cycloparans. The feedstock should be low in sulfur and contain no more than about 3 to 5 percent of oleiins.

Hydrogen chloride is included in the reaction mixture within the range of 0.1 to volume percent in the hydrocarbon phase. More than this amount can be used, but little benefit is derived. lIt is preferred that the hydrogen chloride content of the hydrocarbon phase in the reaction mixture be about 0.5 to 5 volume percent.

The 4isobutane in the hydrocarbon feed to the liquid phase is'omerization reaction is usually in an amount to give a mol ratio with the liquid hydrocarbon ina range of 0.5:1 to 20:1, preferably between 1:1` to 10:1. The ratio of isobutane to normally liquid hydrocarbon determines the products formed in the reaction, and thus the process can be controlled by controlling the amount of isobutane charged to the reaction. At low ratios of isobutane, .the reaction will make some net isobutane, which can be removed from the process with recycleof the remainder. Where such production of isobutane is not desired, the isobutane in the feed can be increased to a point where no net lisobutane is produced, this point being readily maintained in the process by recycling all isobutane in the reaction mixture, thus establishing equilibrium without any complex controls. 'Isobutane can be consumed with the production of higher hydrocarbons by introducing additional outside isobutane and not removing isobutane from the process. In the case of normal heptane as the liquid hydrocarbon feed, the ratio of isobutane to normal heptane at which there is no net consumption or production of isobutane is about 1.3 mols per mol. With higher hydrocarbons, this ratio is somewhat increased.

.Another effect of the isobutane in the feed, as stated above, is that of preserving catalyst Iactivity. At a mol ratio of about 1.3:1 when processing isobutane and normal heptane, the aluminum chloride content of the catalyst complex neither increases nor decreases with use, and thus indicates substantially no catalyst consumption. At a lower isobutane content in the feed, the catalyst de isoinheavier norexceed the butane contents, the percent of aluminum chloride creases in the catalyst complex. With the mal paraihns the isobutane reacted can heavier paran reacted on a mol basis with correspondingly high yields of gasoline range products. The minimum volume of isobutane that must be changed to reduce complex formation to an economic level is dependent to -a limited extent upon the normal paran feed. The minimum volume of isobutane ranges from about percent of the total feed for heptane to about 75 percent for n-decane.` In operating the present process in commercial practice, numerous methods are available for preparing the feed stock. Narrow boiling range cuts of low aromatic and naphthene concentration can be prepared by fractionation and used in the process. This` process can advantageously be used in conjunction with reformer operation by subjecting a reformed gasoline to solvent extraction to remove the aromatics to the desired low figure, and then converting the parainic raffnate by the process of the present invention to upgrade the parains in that raffinate. This sequence of operations is particularly advantageous in that the reforming operation converts naphthenes to aromatics and the solvent extraction removes both the newly formed aromatics `and those originally present in the gasoline. Thus, a feed low in both naphthenes and aromatics can be prepared by processes familiar in refinery operation. In a second method of feed preparation, the reformer effluent can be :contacted with a molecular sieve adsorbent whereby the norm-al parains are removed from the reformed gasoline, -and the unadsorbed hydrocarbons separated from the adsorbent. The molecular sieve can then be regenerated with 'the recovery of the normal parains, and the recovered normal parafns then processed in accordance with the present invent-ion.

Advantages of this invention are illustrated by the following example. The reactants, and their propor tions, and other specific conditions are presented as being typical and should not be construed to limit the invention unduly.

Example IIsobutane is formed by passing n-butane in the vapor phase over a xed bed catalyst of 5 weight percent aluminum chloride on bauxite and in the presence of 3 weight percent HC1 based on the feed. Reaction conditions are as follows:

Temperature F 225 lPressure p.s.i.g 220 Residence time seconds .100 `Liquid hourly space velocity 0.8

. The isomerization etluent is condensed and ashed at 30 p.s.i.a. The vapors formed are recompressed to 225 p.s.i.g., and at la temperature of 125 F. returned to the isomerization zone. The liquid eiluent from the flash has a temperature of 55 F. and the following composition:

Iliquid' volume percent -Propane 1.2 Isobutane 33.9 n-Butane 64.5 Pentanes and higher 0.4

'Ilhis cooled effluent is fed to a liquid phase isomerization reactor at -a rate of 8,750 pounds per hour.

The liquid phase isomerization employs an aluminum chloride-hydrocarbon complex catalyst containing 60 weight percent aluminum chloride.

is fed to the reaction at 2900 pounds per hou-r. Reaction conditions are as follows:

Temperature `F... Pressure p.si a 125 HC1 concentration weght percent 4 Residence time minutes 30 Hydrocarbon/catalyst ratio 2/1 Reaction eluent is settled 'to separate the catalyst. The isomerization product is recovered at 12,750 pounds per hour and has the following composition (HC1 free basis):

Liquid volume percent Propane 0.8 Isobutane 33.5 n-Butane 43.0 Isopentane 4.4 n-Pentane 0.9 Neohexane 1.3 Methylpentanes 3.1 n-Hexane 0.5 Dimethylpentanes `6.1 Methylhexane 5.0 n-Heptane and heavier 1.4

`A `negligible amount of heavy Ifeed complexes with the aluminum chloride catalyst.

Hept-ane at F.

7 are compressed to 150 p.s.i.a. and condensed by heat exchange with water at 70 F. The condensed recycle stream has ya temperature of 100 F. and is returned to the liquid phase isomerization reactor.

Flash bottoms containing 75 percent butanes and lighter and 25 percent pentanes and heavier are withdrawn at a rate of 11,650 pounds per hour and have a temperature of 60 F. These bottoms are passed in heat exchange with the n-heptane feed and are then fractionated to separate four streams, pentanes and heavier which are recovered for use in gasoline blending, n-butane which is recycled to the fixed bed butane isomerization reaction, isobutane yields free of HCl, and an isobutane-HCI mixture which is compressed Vand recycled to the liquid phase isomerization reactor with the overhead from the second flash zone.

As a result of operating according to the above example, catalyst consumption is held to a minimum, the temperature of the liquid phase isomerization is maintained at a relatively low value without using refrigeration, and expensive fractionation steps are eliminated.'

As will be evident to those skilled in the art, various modifications of this invention can be made, or followed, in the light of the foregoing disclosure and discussion, without departing from the. spirit or scope thereof.

I claim:

l. In a combination process wherein butane is first isomerized in the presence of hydrogen chloride to form isobutane which is used in a second isomerization of normally liquid parafiinic hydrocarbons in the presence of hydrogen chloride to conserve the aluminum halide catalyst, the improved method of maintaining the temperature of the'second isomerization ata low value which comprises flashing hydrogen chloride from the effluent fthe first isomerization thereby cooling said isobutane by auto-refrigeration, feeding the thus cooled isobutane to said second isomerization, flashing hydrogen chloride from the efuent of said second isomerization thereby, cooling the effluent of said second isomerization by autorefrigeration, and cooling the normally liquid pa-raflinic hydrocarbon feed to said second isomerization by heat exchange with the thus cooled second isomerization effluent.

2. A process for-isomerizing butane and normal paraffins having from 5 to 12 carbon atoms per molecule which comprises contacting normal butane in a first isomerization zone with aluminum halide in the presencel of hydrogen chloride under isomerizing conditions thereby forming a first product stream comprising Aisobutane and hydrogen chloride, cooling said first product stream by auto-refrigerationfthus'separating hydrogen chloride suitable for recycle to said first isomerization zone and forming a cooled stream comprising isobutane, feeding said cooled isobutane stream to a second isomerization zone containing aluminum halide catalyst and hydrogen chloride, feeding at leastv one normal paraffin .having from 5 to 12 carbon atoms per molecule to said second` isomerization zone, contacting said parains with said'l catalyst in saidsecondzone under isomerizing conditions thereby producing a second product stream comprising isobutane, hydrogen, chloride and isoparafns having from 5 to 8 carbon atoms per moleculecooling said secondy product stream by auto-refrigeration thus separating hy` drogen chloride and isobutane suitable for recycle to said second isomerization zone and forming a cooled product stream, and coolingsaid normal paraffin feed with said cooled product stream.

3. A process according to claim 2 wherein said normalparaffin is heptane and said secondpzone isomerization catalyst is aluminum chloride-hydrocarbon complex.

4. A process for isomerizing butane and normal paraftins having from 5 to 12 carbon atoms per molecule which comprises passing n-butane through an isomerization zone in Contact with a fixed bed aluminum chloride catalyst inthe presence of hydrogenk chloride thus producing al first effluent stream comprising n-butane, isobutane and hydrogen chloride, condensing said first eflluent stream, flashing said first effluent stream to produce a vapor stream comprising hydrogen chloride and a cooled liquid stream. comprising isobutane and n-butane, recycling said vapor stream to said isomerization zone, introducing said cooled liquid stream into a liquid phase isomerization zone using a catalyst of aluminum chloridehydrocarbon complex, introducing a feed stream of normal paraffin having from 5 to l2 carbon atoms per molecule into said liquid phase isomerization zone, withdrawing a second effluent stream from said liquid phase isomerization zone, flashing said second eluent stream to produceV an overhead stream of vapors comprising hydrogen chloride and isobutane and a cooled bottom liquid stream comprising isomerized product, recycling said overhead stream to said liquid phase isomerization zone, and cooling said feed stream by indirect heat exchange with Vsaid bottom stream.

5. A combination process for isomerizing butane and normal paraflins having from 5 to 12 carbon atoms per molecule which comprises passing n-butane through a first isomerization zone in contact with a fixed bed aluminum chloride catalyst in the presence of hydrogen chloride thus producing a first effluent stream comprising n-butane, isobutane and hydrogen chloride, condensing said first eflluent stream, flashing said rst effluent stream to produce a first vapor stream comprising hydrogen chloride and a first cooled liquid stream comprising isobutane, n-butane and hydrogen chloride, condensing said first vapor stream, recycling saidv rst vapor stream to said first isomerization zone, passing said first cooled liquid stream into a second isomerization zone containing a catalyst of aluminum chloride-hydrocarboncomplex, introducing a feed stream of normal paraffin having from 5 to 12 carbon atoms per molecule into said second isomerization zone, withdrawing a second effluent s-tream from said second isomerization zone, settling said stream to form a catalyst phase and a hydrocarbon phase, recycling said catalystphase to said second isomerization zone, flashing said hydrocarbon phase to produce a second vapor stream comprising hydrogen chloride and isobutane and a second cooled liquid stream comprising normal butane, isobutane, and branched parafiins having from 5 to 8 carbon atoms per molecule, condensing said` second vapor stream, returning the condensate to said secondy isomerization zone, and cooling said feed stream by indirect heatv exchange with said second cooled liquid stream.

6, A combination process for isomerizing butane and normal parains having from 5 to 12 carbon atoms per molecule which comprises passing n-butane through a first isomerization zone in contact with a fixed bed aluminum chloride catalyst in the presence of yhydrogen chloride thus producing a first effluent stream comprisingn-butane, isobutane and hydrogen chloride, condens. ing said first effluent stream, flashing said `first eflluent stream to produce a first vapor stream comprising hydroing a catalyst of aluminum chloride-hydrocarbon com-l plex, introducing a feed stream of normal parafhn having from 5 to l2 carbon atoms per molecule into said second isomerization zone, withdrawing a second effluent stream from said second isomerization zone, settling said stream to form a catalyst phase and a hydrocarbon phase,l

recycling said Vcatalyst phase to' saidsecond isomerization zone, hashingV said hydrocarbon phase to produce a second vaporI stream comprising hydrogen chloride and isobutan'e and a second cooled liquid stream comprising normal-butane, isobutane, and branched paraflins4 having from 5 to 8 carbon atomsv per molecule, condensing said second vapor stream, returning the condensate to said second isomerization zone, cooling said feed stream by indirect heat exchange with said second cooled liquid stream, frac-donating said second liquid stream to produce a normal butane stream, an isobutane-hydrogen chloride stream, and a product stream comprising branched para'ns having from 5 to 8 carbon atoms per molecule, returning said n-butane stream to said rst isomerization zone, and returning said isobutane-hydrogen chloride stream to said second isomerization zone.

7. The process according to claim 6 wherein said normal paran feed is n-heptane.

8. The process according to claim 7 wherein said isobutane/n-heptane ratio in the feed to second isomerization zone is in the range of 0.5:1 to 5:1 on a mol basis.

5 ture of said second liquid stream is in the .range of 40 to 80 F.

References Cited in the le of this patent UNITED STATES PATENTS Re. 22,146 Goldsby et a1 July 28, 1942 2,256,880 `Goldsby et a1 Sept. 23, 1941 2,306,253 McMillan Dec. 22, 1942 2,386,784 Fragen Oct. 16, 1945 Gwynn et a1. Nov. 21, 1950 

1. IN A COMBINATION PROCESS WHEREIN BUTANE IS FIRST ISOMERIZED IN THE PRESENCE OF HYDROGEN CHLORIDE TO FORM ISOBUTANE WHICH IS USED IN A SECOND ISOMERIZATION OF NORMALLY LIQUID PARAFFINIC HYDROCARBONS IN THE PRESENCE OF HYDROGEN CHLORIDE TO CONSERVE THE ALUMINUM HALIDE CATALYST, THE IMPROVED METHOD OF MAINTAINING THE TEMPERATURE OF THE SECOND ISOMERIZATION AT A LOW VALUE WHICH COMPRISES FLASHING HYDROGEN CHLORIDE FROM THE EFFLUENT OF THE FIRST ISOMERIZATION THEREBY COOLING SAID ISOBUTANE BY AUTO-REFRIGERATION, FEEDING THE THUS COOLED ISOBUTANE TO SAID SECOND ISOMERIZATION, FLASHING HYDROGEN CHLORIDE FROM THE EFFLUENT OF SAID SECOND ISOMERIZATION THEREBY, COOLING THE EFFLUENT OF SAID SECOND ISOMERIZATION BY AUTOREFRIGERATION, AND COOLING THE NORMALLY LIQUID PARAFFINIC HYDROCARBON FEED TO SAID SECOND ISOMERIZATION BY HEAT EXCHANGE WITH THE THUS COOLED SECOND ISOMERIZATION EFFLUENT. 